Prosthetic foot

ABSTRACT

A prosthetic foot comprising an internal keel ( 1 ) and an encapsulation material ( 2 ). The keel ( 1 ) is made of two parts ( 3, 4 ), namely an elastic ankle ( 3 ) and an elastic blade ( 4 ), to ensure a behaviour of the prosthesis as close as possible to the biomechanics of a sound human foot (plantar flexion, dorsiflexion, inversion, eversion). The materials and design used for the keel ( 1 ) allow storing and releasing strain energy at the right phases of the gait cycle. Elastomeric foams act as safety features in specific areas to prevent keel overloading. The keel ( 1 ) is preferably encapsulated into two types of foam to fill internal space and as cosmetic feature as it has a human foot shape.

FIELD OF INVENTION

The invention relates to a prosthetic foot comprising a keel embedded in a material, e.g. a foam.

STATE OF THE ART

Examples of such prosthetic feet are disclosed in the following patent documents: EP 0 648 479 A1, U.S. Pat. Nos. 5,116,385, 4,645,509 or 5,156,632.

GENERAL DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a prosthetic foot having improved biomechanical properties.

The prosthetic foot according to the invention is defined in the claims.

It comprises a keel embedded in an encapsulation material; said keel comprising a U-shaped elastic ankle, preferably made of an injection-moulded LFT composite, and an elastic blade that is fixed to the bottom part of the ankle element, said encapsulation material may advantageously comprise an internal foam that at least partially encapsulates the keel and an external foam that encapsulates the internal foam, the external foam having a higher density than the internal foam density.

Biomechanically, the prosthetic foot according to the invention provides biomechanics that is very similar to the one of a sound human foot (plantar flexion, dorsiflexion, inversion, eversion). The materials and design used for the keel allow storing and releasing strain energy at the right phases of the gait cycle. The encapsulation material acts as a safety feature to prevent keel overloading and as cosmetic feature as it has a human foot shape.

The LFT composite preferably comprises 15% to 70% volume fraction of fibres with a length ranging from 1 mm to 15 mm.

The elastic blade may advantageously be made of a composite that comprises 40% to 65% volume fraction of fibres which are typically longer than 50 mm.

In a preferred embodiment, at least an important part of the ankle element is encapsulated in low density foam (typically<0.7 g/cm³) , said foam being overmoulded by injection moulding, casted or glued using an adhesive.

In a preferred embodiment according to the invention the prosthetic foot includes an overload protection system to prevent damage of the prosthetic foot in case of severe loading during use. The overload protection system includes at least one spacer, preferably made of an elastomeric material, that is arranged between two overlapping parts of the keel 1.

The prosthetic foot is designed in a way it can be bolted to a prosthetic leg from the sole surface and through its whole internal structure like most SACH (Solid Ankle Cushion Heel) feet available on the market.

DETAILED DESCRIPTION OF THE INVENTION

The invention will be better understood in the present chapter, with a non-limiting example illustrated by the following figures:

FIG. 1 shows a keel according to the invention

FIG. 2 shows a complete prosthetic foot (cross-sectional view) that includes the keel of FIG. 1.

NUMERICAL REFERENCES USED IN THE FIGURES

-   1. Keel -   2. Encapsulation material -   3. Ankle -   4. Elastic blade -   5. Ankle upper branch -   6. Ankle lower branch -   7. Forefoot -   8. Foot bottom -   9. Lower branch free end -   10. Blade central area -   11. Protection system element -   12. Heel -   13. 1^(st) overload protection area -   14. 2^(nd) overload protection area -   15. Shell

The keel 1 (see both figures) is essentially made of two elements, namely:

-   -   An elastic partly slotted ankle 3 made of an injection-moulded         thermoplastic composite including 15% to 70% volume fraction of         fibres with a length preferably ranging from 1 mm to 15 mm, the         fibres being usually carbon fibres or glass fibres. The         composite thermoplastic matrix may be composed of a         thermoplastic polymer matrix such as, but not limited to PE, PA,         PP, PEI, PEKK, PEEK, PET, PI, ABS, POM, PM MA, PPA, PPS.     -   An elastic partly slotted blade 4 made of a long         fibre-reinforced thermoset or thermoplastic composite including         40% to 65% volume fraction of fibres which are preferably longer         than 50 mm, the fibres being preferably carbon fibres, glass         fibres, aramid or basalt fibres. The composite matrix may be         either a thermoset polymer (epoxy, polyester, vinyl ester) or a         thermoplastic one (PE, PA, PP, PEI, PEKK, PET, PI, ABS, POM,         PMMA). The thermoset composite can be processed by wet layup,         vacuum bagging, autoclave, compression moulding or resin         transfer moulding. Thermoplastic composites can be processed by         compression moulding, resin transfer moulding or any other         suitable process.

In the illustrated example (see FIG. 2), the keel 1 is embedded in an encapsulation material 2 and both objects 1, 2 being contained within a shell 15 having the shape of a normal foot.

The ankle 3 has roughly a horizontal U-shape with an upper branch 5 and a longer lower branch 6.

The upper branch 5 has a vertical extension 11 that forms a part of an overload protection system that will be described below.

The free end 9 of the lower branch 6 is fixed to the blade central area 10.

In the illustrated example, bolts are used for the fixation, but any other suitable fixation means may be used.

The foot prosthesis, by combination of the elastic ankle 3 and elastic blade 4, features biomechanical movements (plantar, dorsiflexion, inversion, eversion) and heel shock absorption thanks to their elastic behaviour and a longitudinal slit in the two parts.

As mentioned previously, ankle 3 and 4 are slotted, i.e. they contain a longitudinal slot.

Such slots increase the flexibility of the objects. The invention is of course not limited to such a configuration. Slots are not mandatory. Any other way to increase the flexibility could also be used.

The foot prosthesis features energy storage and release (a.k.a. ESAR in the prosthetics jargon) with an efficiency above 85%, said energy storage and release taking part in similar proportions in both parts.

The ankle 3 and heel 12 areas may include overload protection systems to prevent damage of the prosthetic foot in case of severe loading during use, the overload protection systems being based on a blocking mechanism during plantar and dorsiflexion, the blocking mechanism using a spacer, made e.g. of an elastomeric foam (thermoset or thermoplastic) with a specific and controlled compaction point. The spacer may be made from the same material as the encapsulation material 2. In this latter case, the spacer material has a higher density than the density of the surrounding encapsulation material. The spacers are preferably in an area 13 that is located between the vertical extension 11 and the blade central area 10 or in an area 14 that is located between the ankle 3 rear part and the blade 4.

The low-density foam is encapsulated in a high-density polymer foam (typically>0.7 g/cm³), the foam being thermoset or thermoplastic and is used as an external shell to protect internal parts. This external shell has the proportions and aspect of a human foot (with or without a split between the big toe and others).

Typical Shore hardness of used foams ranges from 35 Shore A to 70 Shore A.

The invention is of course not limited to the illustrated example. 

1. Prosthetic foot comprising a keel embedded in an encapsulation material; said keel comprising two separate elements that are fixed to each other, namely: an horizontal U-shaped elastic ankle oriented in a way as having the two branches of said U pointed towards the forefoot, an elastic blade that extends along the foot bottom; wherein the ankle lower branch free end is fixed to the blade central area.
 2. Prosthetic foot according to claim 1 wherein the ankle lower branch is longer than the ankle upper branch.
 3. Prosthetic foot according to claim 1 wherein the ankle is made of an injection-moulded LFT composite
 4. Prosthetic foot according to claim 3 wherein said LFT composite comprises 15% to 70% volume fraction of fibres with a length ranging from 1 mm to 15 mm.
 5. Prosthetic foot according to claim 3 wherein said elastic blade is made of a composite that comprises 40% to 65% volume fraction of fibres which are typically longer than 50 mm.
 6. Prosthetic foot according to claim 1 including an overload protection system to prevent damage of the prosthetic foot in case of severe loading during use.
 7. Prosthetic foot according to claim 6 wherein said protection system comprises a spacer that is arranged in at least one area that is located between two overlapping parts of the keel.
 8. Prosthetic foot according to claim 6 wherein said protection system comprises a vertical element that forms an extension of the ankle upper branch.
 9. Prosthetic foot according to claim 8 wherein said spacer is arranged in an area that is located between the vertical element and the blade central area.
 10. Prosthetic foot according to claim 7 comprising another spacer that is arranged in an area that is located between the rear part of the ankle and the blade.
 11. Prosthetic foot according to claim 7, wherein said spacer(s) is/are made of a different material than said encapsulation material.
 12. Prosthetic foot according to claim 7, wherein said spacer(s) is/are made of the encapsulation material but said material has a higher density than the density of the encapsulating material that fills the non-specific of the foot internal space. 